In the past, sand control methods have been dominated by gravel packing outside of downhole screens. The idea was to fill the annular space outside the screen with sized gravel to prevent the production of undesirable solids (sand) from the formation. More recently, with the advent of tubular expansion technology, it was thought that the need for gravel packing could be eliminated if a screen or screens could be expanded in place to eliminate the surrounding annular space that had heretofore been packed with gravel. Problems arose with the screen expansion technique as a replacement for gravel packing because of wellbore shape irregularities. A fixed swage would expand a screen only a fixed amount. Problems still included that a washout in the wellbore would still leave a large annular space outside the screen. Conversely, a tight spot in the wellbore could create the risk of sticking the fixed swage.
One improvement of the fixed swage technique was to use various forms of flexible swages. In theory, these flexible swages were compliant so that in a tight spot they would flex inwardly and reduce the chance of sticking the swage. On the other hand, if there was a void area, the same problem persisted in that the flexible swage had a finite outer dimension to which it would expand the screen. Therefore, the use of flexible swages still left the potential problem of annular gaps outside the screen with a resulting undesired production of solids when the well was put on production from that zone.
Prior designs of screens have used a pre-compressed mat held by a metal sheath that is then subjected to a chemical attack when placed in the desired location downhole. The mat is then allowed to expand from its pre-compressed state. The screen per se is not expanded. This design is described in U.S. Pat. Nos. 2,981,332 and 2,981,333. U.S. Pat. No. 5,667,011 shows a fixed swage expanding a slotted liner downhole. U.S. Pat. Nos. 5,901,789 and 6,012,522 show well screens being expanded. U.S. Pat. No. 6,253,850 shows a technique of inserting one solid liner in another already expanded slotted liner to blank it off and the use of rubber or epoxies to seal between the liners. U.S. Pat. No. 6,263,966 shows a screen with longitudinal pleats being expanded downhole. U.S. Pat. No. 5,833,001 shows rubber cured in place to make a patch after being expanded with an inflatable. Finally, U.S. Pat. No. 4,262,744 is of general interest as a technique for making screens using molds.
U.S. Pat. No. 7,318,481 describes a screen assembly that includes a material that conforms to the borehole shape after insertion. The assembly comprises a compliant layer that takes the borehole shape on expansion. The outer layer is formed having holes to permit production flow. The material that is selected preferably swells with heat and in one non-limiting embodiment preferably comprises a shape memory foam that is thermoset. The base pipe may have a screen over it to act as an underlayment for support of the conforming layer or alternatively for screening. The conforming layer can expand by itself or expansion may also occur from within the base pipe. This design could be improved if the expansion of the compliant layer were activated by heat locally at its downhole location to a temperature greater than that experienced by the screen assembly on its trip into the hole. If the compliant layer experiences too much heating in advance of placement, it will deploy prematurely, and in most cases be difficult or impossible to dislodge.
A difficulty with supplying heat downhole by injecting a heated medium is that the heat will be dissipated during transmission and insufficient heat will be delivered to the desired site. Methods are known for providing heat only locally downhole, but they each have difficulties. Downhole heaters, such as electrically-powered heaters, such as a wireline deployed electric heater, or a battery fed heater, may generally lack sufficient power (amperage) to provide the necessary heat for deployment. Downhole combustion processes are also known to generate heat. However, most exothermic oxidation/combustion reactions require temperatures that would compromise mud stability, if not tubular integrity, and would tend to be difficult to initiate and would be problematic to formulate as a liquid or mud for downhole use. Again, initiating the reaction at the surface would tend to expend and dissipate most of the heat before placement in the target or the mud for downhole use. Hydration of acidic electrolytes (such as aluminum chloride, AlCl3) or acids would also generate heat, but would be expected to be corrosive and at high temperatures could compromise the integrity of the tubular goods, tools, screens and other equipment in many circumstances. For instance, hydration of aluminum chloride would produce a product environment of about pH 0.8, as contrasted with using NaOH, which would generally yield a product environment of about pH 14. There are also heat generating reactions that can be timed through control of the reaction rate through manipulation of pH and other methods such as processes like N-SITU developed by Shell Oil Co. This technology is found in U.S. Pat. Nos. 4,178,993; 4,219,083; 4,289,633; and 4,330,037. This method is a surface-mixed reaction that must be carefully timed with pump rate and the like in order for the heat liberation to occur in a specific zone of interest. While this operation can be accomplished by those skilled in the art, unforeseen circumstances can cause last minute disruptions to this scheduled treatment, and the heat can be liberated in an undesired location in the wellbore.
It would thus be very desirable and important to discover a method and apparatus for deploying a compliant layer only at a particular temperature or temperature range at a particular location downhole.